Layered materials with improved magnesium intercalation for rechargeable magnesium ion cells

ABSTRACT

Electrochemical devices which incorporate cathode materials that include layered crystalline compounds for which a structural modification has been achieved which increases the diffusion rate of multi-valent ions into and out of the cathode materials. Examples in which the layer spacing of the layered electrode materials is modified to have a specific spacing range such that the spacing is optimal for diffusion of magnesium ions are presented. An electrochemical cell comprised of a positive intercalation electrode, a negative metal electrode, and a separator impregnated with a nonaqueous electrolyte solution containing multi-valent ions and arranged between the positive electrode and the negative electrode active material is described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of co-pending U.S.provisional patent application Ser. No. 61/617,512, filed Mar. 29, 2012,which application is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY FUNDED RESEARCH OR DEVELOPMENT

This invention was made with government support under award numberDE-AR0000062, awarded by Advanced Research Projects Agency-Energy(ARPA-E), U.S. Department of Energy. The government has certain rightsin the invention.

FIELD OF THE INVENTION

The invention relates to electrode materials in general and particularlyto electrode materials useful in secondary batteries that employ Mg intheir electrolytes.

BACKGROUND OF THE INVENTION

A variety of new secondary electrochemical cells that exhibit highenergy density have been demonstrated. However, commercial systemsremain primarily based on lithium ion (Li-ion) chemistry. Such cellsfrequently consist of a layered transition metal oxide cathode material,an anode-active lithium metal or lithium intercalation or alloy compoundsuch as graphitic carbon, tin and silicon, and an electrolytic solutioncontaining a dissolved lithium-based salt in an aprotic organic orinorganic solvent or polymer. Today there is great demand for energystorage devices that exhibit higher volumetric and gravimetric energydensity when compared to commercially available lithium ion batteries.Consequently an increasingly sought after route to meeting this demandhigher energy density is to replace the monovalent cation lithium (Li⁺)with multi-valent ions, such as divalent magnesium cations (Mg²⁺),because these ions can enable many times the charge of Li⁺ to betransferred per ion.

Furthermore, alkali metals, and lithium in particular, have numerousdisadvantages. Alkali metals are expensive. Alkali metals are highlyreactive. Alkali metals are also highly flammable, and fire resultingfrom the reaction of alkali metals with oxygen, water or other activematerials is extremely difficult to extinguish. Lithium is poisonous andcompounds thereof are known for their severe physiological effects, evenin minute quantities. As a result, the use of alkali metals requiresspecialized facilities, such as dry rooms, specialized equipment andspecialized procedures.

Gregory et al., “Nonaqueous Electrochemistry of Magnesium; Applicationsto Energy Storage” J. Electrochem. Soc., Vol. 137, No. 3, March 1990discloses Co₃O₄, Mn₂O₃, Mn₃O₄, MoO₃, PbO₂, Pb₃O₄, RuO₂, V₂O₅, WO₃, TiS₂,VS₂, ZrS₂, MoB₂, TiB₂, and ZrB₂ as positive electrode materials for amagnesium battery. However, only the first cycle discharge is shown andall materials exhibit significant polarization for medium currentdensities.

Novak et al., “Electrochemical Insertion of Magnesium in Metal Oxidesand Sulfides from Aprotic Electrolytes,” JECS 140 (1) 1993 disclosesTiS₂, ZrS₂, RuO₂, Co₃O₄ and V₂O₅ as positive electrode materials of amagnesium battery. However, only layered V₂O₅ shows promising capacityand reversibility. Furthermore, Novak et al. show that Mg²⁺ insertioninto this oxide depends on the ratio between the amounts of H₂O and Mg²⁺as well as on the absolute amount of H₂O in the electrolyte. Accordingto Novak, water molecules preferentially solvate Mg²⁺ ions, whichfacilitate the insertion process by co-intercalation.

Novak et al., “Electrochemical Insertion of Magnesium into HydratedVanadium Bronzes” Electrochem. Soc., Vol. 142, No. 8, 1995 disclosesMg²⁺ insertion into layered vanadium bronzes, MeV₃O₈(H2O)_(y) where(Me=Li, Na, K, Ca_(0.5), and Mg_(0.5)). Variations in the content ofbound lattice water in the bronzes were found to be responsible for adifference in the electrochemical properties of the same startingmaterial dried at different temperatures. The presence of this water wasdeemed essential but the lattice water is removed during cycling afterwhich the capacity deteriorates. Furthermore, attempts to cycle thecompounds in dry electrolytes failed. The beneficial effect of water wasspeculated to be due to its solvation of the Mg²⁺ ion.

Le et al., “Intercalation of Polyvalent Cations into V₂O₅ Aerogels”Chem. Mater. 1998, 10, 682-684 discloses multi-valent ion insertion intoV₂O₅ areogels where the small diffusion distances and high surface areaare regarded as beneficial for multi-valent intercalation. X-raydiffraction of the aerogel shows an interlayer spacing of 12.5 A (due toretaining acetone), as compared to the 8.8 A characteristic of theV₂O₅*0.5H₂O xerogel.

Amatucci et al., “Investigation of Yttrium and Polyvalent IonIntercalation into Nanocrystalline Vanadium Oxide,” J Electrochem Soc,148(8), A940-A950, Jul. 13, 2001, show reversible intercalation ofseveral multi-valent cations (Mg²⁺, Ca²⁺, Y³⁺) into nano-metric layeredV₂O₅ but with significant polarization (e.g., energy loss) and at a lowrate of 0.04 C which signifies the low diffusivity of the Mg ions.

The current, proven state of the art high energy, rechargeable Mg cellis described by Aurbach et al., U.S. Pat. No. 6,316,141, issued Nov. 13,2001, as a cell comprised of a magnesium metal anode, a “Chevrel” phaseactive material cathode, and an electrolyte solution derived from anorganometallic complex containing Mg. Chevrel compounds are a series ofternary molybdenum chalcogenide compounds first reported by R. Chevrel,M. Sergent, and J. Prigent in J. Solid State Chem. 3, 515-519 (1971).The Chevrel compounds have the general formula M_(x)Mo₆X₈, where Mrepresents any one of a number of metallic elements throughout theperiodic table; x has values between 1 and 4, depending on the Melement; and X is a chalcogen (sulfur, selenium or tellurium).Furthermore, in E. Levi et al, “New Insight on the Unusually High IonicMobility in Chevrel Phases,” Chem Mat 21 (7), 1390-1399, 2009, theChevrel phases are described as unique materials which allow for a fastand reversible insertion of various cations at room temperature.

Michot et al., U.S. Pat. No. 6,395,367, issued May 28, 2002, is said todisclose ionic compounds in which the anionic load has been delocalized.A compound disclosed by the invention includes an anionic portioncombined with at least one cationic portion M^(m+) in sufficient numbersto ensure overall electronic neutrality; the compound is furthercomprised of M as a hydroxonium, a nitrosonium NO⁺, an ammonium NH₄ ⁺, ametallic cation with the valence m, an organic cation with the valencem, or an organometallic cation with the valence m. The anionic load iscarried by a pentacyclical nucleus of tetrazapentalene derivativebearing electroattractive substituents. The compounds can be usednotably for ionic conducting materials, electronic conducting materials,colorant, and the catalysis of various chemical reactions.

U.S. Pat. No. 6,426,164 B1 to Yamaura et al., issued Jul. 30, 2002, issaid to disclose a non-aqueous electrolyte battery capable of quicklydiffusing magnesium ions and improving cycle operation resistance,incorporating a positive electrode containing Li_(x)MO₂ (where M is anelement containing at least Ni or Co) as a positive-electrode activematerial thereof; a negative electrode disposed opposite to the positiveelectrode and containing a negative-electrode active material whichpermits doping/dedoping magnesium ions: and a non-aqueous electrolytedisposed between the positive electrode and the negative electrode andcontaining non-aqueous solvent and an electrolyte constituted bymagnesium salt, wherein the value of x of Li_(x)MO₂ satisfies a range0.1≦x≦0.5. It is also said that for Li concentrations x ≦0.1, the hostmaterial becomes unstable and for higher Li concentrations x ≧0.5, thereare not enough available Mg lattice sites available. Specifically, thereis no mention of interlayer distance.

Michot et al., U.S. Pat. No. 6,841,304, issued Jan. 11, 2005, is said todisclose novel ionic compounds with low melting point whereof the oniumtype cation having at least a heteroatom such as N, O, S or P bearingthe positive charge and whereof the anion includes, wholly or partially,at least an ion imide such as (FX¹ O)N⁻ (OX² F) wherein X¹ and X² areidentical or different and comprise SO or PF, and their use as solventin electrochemical devices. Said composition comprises a salt whereinthe anionic charge is delocalised, and can be used, inter alia, aselectrolyte.

U.S. Patent Application Publication No. 20090068568 A1 (Yamamoto et al.inventors), published on Mar. 12, 2009, is said to disclose a magnesiumion containing non-aqueous electrolyte in which magnesium ions andaluminum ions are dissolved in an organic etheric solvent, and which isformed by: adding metal magnesium, a halogenated hydrocarbon RX, analuminum halide AlY₃, and a quaternary ammonium salt R¹R²R³R⁴N⁺Z⁻ to anorganic etheric solvent; and applying a heating treatment while stirringthem (in the general formula RX representing the halogenatedhydrocarbon, R is an alkyl group or an aryl group, X is chlorine,bromine, or iodine, in the general formula AlY₃ representing thealuminum halide, Y is chlorine, bromine, or iodine, in the generalformula R¹R²R³R⁴N⁺Z⁻ representing the quaternary ammonium salt, R¹, R²,R³, and R⁴ represent each an alkyl group or an aryl group, and Zrepresents chloride ion, bromide ion, iodide ion, acetate ion,perchlorate ion, tetrafluoro borate ion, hexafluoro phosphate ion,hexafluoro arsenate ion, perfluoroalkyl sulfonate ion, or perfluoroalkylsulfonylimide ion. These additives are aimed at increasing the stabilityof the electrolyte in atmospheric air and facilitate the productionprocess for said electrolytes.

U.S. Patent Application Publication No. 20100136438 A1 (Nakayama et al.inventors), published Jun. 3, 2010, is said to disclose a magnesiumbattery that is constituted of a negative electrode, a positiveelectrode and an electrolyte. The negative electrode is formed ofmetallic magnesium and can also be formed of an alloy. The positiveelectrode is composed of a positive electrode active material, forexample, a metal oxide, graphite fluoride ((CF)_(n)) or the like, etc.The electrolytic solution is, for example, a magnesium ion containingnonaqueous electrolytic solution prepared by dissolving magnesium(II)chloride (MgCl₂) and dimethylaluminum chloride ((CH₃)₂AlCl) intetrahydrofuran (THF). In the case of dissolving and depositingmagnesium by using this electrolytic solution, they indicate that thefollowing reaction proceeds in the normal direction or reversedirection.

According to this, there are provided a magnesium ion-containingnonaqueous electrolytic solution having a high oxidation potential andcapable of sufficiently bringing out excellent characteristics ofmetallic magnesium as a negative electrode active material and a methodfor manufacturing the same, and an electrochemical device with highperformances using this electrolytic solution.

U.S. Patent Application Publication No. 20110111286 A1 (Yamamoto el at.inventors), published on May 12, 2011, is said to disclose a nonaqueouselectrolytic solution containing magnesium ions which shows excellentelectrochemical characteristics and which can be manufactured in ageneral manufacturing environment such as a dry room, and anelectrochemical device using the same are provided. A Mg battery has apositive-electrode can, a positive-electrode pellet made of apositive-electrode active material or the like, a positive electrodecomposed of a metallic net supporting body, a negative-electrode cup, anegative electrode made of a negative-electrode active material, and aseparator impregnated with an electrolytic solution and disposed betweenthe positive-electrode pellet and the negative-electrode activematerial. Metal Mg, an alkyl trifluoromethanesulfonate, a quaternaryammonium salt or/and a 1,3-alkylmethylimidazolium salt, more preferably,an aluminum halide are added to an ether system organic solvent and arethen heated, and thereafter, more preferably, a trifluoroboraneethercomplex salt is added thereto, thereby preparing the electrolyticsolution. By adopting a structure that copper contacts thepositive-electrode active material, the electrochemical device can begiven a large discharge capacity.

Nazar et al, “Insertion of Poly(p-phenylenevinylene) in Layered MoO₃ ”,J. Am. Chem. Soc. 1992, 114, 6239-6240 discloses insertion of highmolecular weight PPV into a layered oxide by intercalating the PPVprecursor polymer between the layers of MoO₃, by ion exchange. The layerspacing was reported to increase from 6.9 Å to 13.3 Å. Noelectrochemical investigations of the host material were performed.

Nazar et al, “Hydrothermal Synthesis and Crystal Structure of a NovelLayered Vanadate with 1,4-Diazabicyclo[2.2.2]octane as theStructure-Directing Agent: C₆H₁₄N₂—V₆O₁₄.H₂O” Chem. Mater. 1996, 8, 327discloses Li insertion into organic cation (C₆H₁₂N₂ or‘DABCO’)-templated vanadium oxide resulting from hydrothermal synthesis.The host crystal structure possesses a structure composed of a newarrangement of edge-shared VO₅ square pyramids that are corner-sharedwith VO₄ tetrahedra to form highly puckered layers, between which theDABCO cations are sandwiched. The results show that Li insertion ishindered in the DABCO-filled host and improved performance is obtainedwhen the DABCO ion is removed.

Goward et al, “Poly(pyrrole) and poly(thiophene)/vanadium oxideinterleaved nanocomposites: positive electrodes for lithium batteries”,Electrochimica Acta, 43, 10-11, pp. 1307, 1998 reports on synthesis andelectrochemical investigation of conductive polymer-V₂O₅ nanocompositesthat have a structure comprised of layers of polymer chains interleavedwith inorganic oxide lamellae. It was found that for modified[PANI]-V₂O₅, polymer incorporation resulted in better reversibility, andincreased Li capacity in the nanocomposite compared to the original V₂O₅xerogel. For PPY and PTH nanocomposites, the electrochemical responsewas highly dependent on the preparation method, nature of the polymer,and its location. In conclusion, Goward et al note that the results,though promising, were still short of theoretical expectations.

Chirayil et al, ‘Synthesis and characterization of a new vanadium oxide,TMA-V₈O₂O’ J. Mater. Chem., 1997, 7(11), 2193-2195 discloses synthesisof a layered vanadium oxide with a new monoclinic structure in which thetetramethylammonium ions reside between the vanadium oxide layers. Thepowder X-ray diffraction pattern indicate that this new vanadium oxidehas an interlayer spacing of 11.5 Angstrom. Electrochemicalinvestigation of the compound indicates that Li insertion is hindereddue to the TMA ions between the layers.

Lutta et al, “Solvothermal synthesis and characterization of a layeredpyridinium vanadate, C₅H₆N—V₃O₇” J. Mater. Chem., 2003, 13, 1424-1428reports on synthesis and properties of a layered vanadate which has anaromatic intercalate (pyridinium ion) between the vanadium oxide layers:pyH-V₃O₇. Chemical lithiation show some reactivity with Li but betterperformance was obtained when the pyridinium was removed from thevanadate. Indeed, Lutta et al concludes with saying that none of thearomatic V₃O₇ based structures (TMA-V₃O₇, MA-V₃O₇, pyH—V₃O₇) or theirdecomposition products lead to electrochemically interesting materials.

The results described above show that slow diffusion of multi-valentions in layered cathode materials is a limiting factor in rechargeablemulti-valent electrochemical cells.

Furthermore, the results above also show that it is commonly believedthat organic-inorganic hybrid host materials do not improveintercalation performance, specifically for lithium ions.

There is a need for systems and methods for making improved positiveelectrode layered materials with high energy density as well as facileMg ion diffusion.

SUMMARY OF THE INVENTION

According to one aspect, the invention features an energy-storageapparatus. The energy-storage apparatus comprises an anode configured toaccept Mg ions from an electrolyte and to release Mg-ions to theelectrolyte, the anode having at least one anode electrical connectionon an external surface of the energy-storage apparatus, and having atleast one anode surface within the energy-storage apparatus; a cathodecomprising a layered crystalline compound comprising a transition metal,wherein an interlayer metal-metal distance in the layered crystallinecompound is 4.8 Angstrom or more, the layered crystalline compoundhaving at least one cathode electrical connection on an external surfaceof the energy-storage apparatus and having at least one cathode surfacewithin the energy-storage apparatus; and the electrolyte comprising amagnesium-bearing electrolyte in contact with the at least one anodesurface within the energy-storage apparatus, and in contact with the atleast one cathode surface within the energy-storage apparatus.

In one embodiment, the cathode comprising a layered crystalline compoundcomprises a compound having the chemical formula Mg_(a)M_(b)X_(y),wherein M is a metal cation or a mixture of metal cations, X is an anionor mixture of anions, a is in the range of 0 to about 2, b is in therange of about 1 to about 2, and y ≦9.

In another embodiment, at least one of the anode and the cathode furthercomprises an electronically conductive additive.

In yet another embodiment, the at least one of the anode and the cathodefurther comprises a polymer binder.

In still another embodiment, the anode configured to accept and releaseMg-ions comprises a material selected from the group consisting of Mg,Mg alloys AZ31, AZ61, AZ63, AZ80, AZ81, AZ91, AM50, AM60, Elektron 675,ZK51, ZK60, ZK61, ZC63, M1A, ZC71, Elektron 21, Elektron 675, Elektron,Magnox, and Mg alloys containing at least one of the elements Al, Ca,Bi, Sb, Sn, Ag, Cu, and Si.

In a further embodiment, the anode configured to accept and releaseMg-ions comprises insertion materials including one or more of AnataseTiO₂, rutile TiO₂, Mo₆S₈, FeS₂, TiS₂, and MoS₂ and combinations thereof.

In yet a further embodiment, the wherein at least one of the cathode andthe anode comprises a carbonaceous material.

In an additional embodiment, the energy-storage apparatus is a secondarybattery.

According to another aspect, the invention relates to an energy-storageapparatus. The energy-storage apparatus, comprises an anode configuredto accept Mg ions from an electrolyte and to release Mg-ions to theelectrolyte, the anode having at least one anode electrical connectionon an external surface of the energy-storage apparatus, and having atleast one anode surface within the energy-storage apparatus; a cathodecomprising a layered crystalline compound comprising a deliberatelyadded specie or species so that a layer spacing of the layeredcrystalline compound is modified to allow for magnesium ion diffusionsufficient to support at least a C/5 discharge rate of the energystorage apparatus, the layered crystalline compound having at least onecathode electrical connection on an external surface of theenergy-storage apparatus and having at least one cathode surface withinthe energy-storage apparatus; and the electrolyte comprising amagnesium-bearing electrolyte in contact with the at least one anodesurface within the energy-storage apparatus, and in contact with the atleast one cathode surface within the energy-storage apparatus.

In one embodiment, a layer spacing of the layered crystalline compoundis modified to allow for magnesium ion diffusion sufficient to supportat least a C/15 discharge rate of the energy storage apparatus.

In another embodiment, the energy-storage apparatus is a secondarybattery.

In yet another embodiment, a shortest metal-metal inter-layer distancein the layered crystalline compound is larger than 4.8 Angstrom.

In still another embodiment, a shortest metal-metal inter-layer distancein the layered crystalline compound is smaller than 8 Angstrom.

In a further embodiment, a shortest metal-metal inter-layer distance inthe layered crystalline compound is smaller than 12 Angstrom.

In yet a further embodiment, the cathode comprising a layeredcrystalline compound comprises a compound having the chemical formulaMg_(a)M_(b)X_(y), wherein M is a metal cation, or mixture of metalcations and X is an anion or mixture of anions, and a is in the range of0 to about 2, b is in the range of about 1 to about 2, and y ≦9.

In an additional embodiment, at least one of the anode and the cathodefurther comprises an electronically conductive additive.

In one more embodiment, at least one of the anode and the cathodefurther comprises a polymer binder.

In still a further embodiment, the anode configured to accept andrelease Mg-ions comprises a material selected from the group consistingof Mg, Mg alloys AZ31, AZ61, AZ63, AZ80, AZ81, AZ91, AM50, AM60,Elektron 675, ZK51, ZK60, ZK61, ZC63, M1A, ZC71, Elektron 21, Elektron675, Elektron, Magnox, and Mg alloys containing at least one of theelements Al, Ca, Bi, Sb, Sn, Ag, Cu, and Si.

In one more embodiment, the anode configured to accept and releaseMg-ions comprises insertion materials selected from the group ofinsertion materials consisting of Anatase TiO₂, rutile TiO₂, Mo₆S₈,FeS₂, TiS₂, and MoS₂ and combinations thereof.

In still a further embodiment, at least one of the cathode and the anodecomprises a carbonaceous material.

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the drawings described below, and the claims. The drawingsare not necessarily to scale, emphasis instead generally being placedupon illustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1A is a schematic diagram of a layered material with Mg ionssituated in the layer and the shortest metal-metal inter-layer centerdistance indicated.

FIG. 1B is a schematic diagram of a layered material having a firstplurality of layers of inorganic material separated by a secondplurality of units of an organic species situated on intervening planes.

FIG. 2 is a graph of calculated diffusivity by first principles nudgedelastic band calculations for a single Mg ion in layered V₂O₅ as afunction of the metal-metal center layer distance. The equilibriumun-modified materials layer distance is specified as well as theestimated 1C rate performance for a representative 100 nm radiuselectrode particle.

FIG. 3 is a graph of calculated diffusivity by first principles nudgedelastic band calculations for a single Mg ion in layered MnO₂ as afunction of the metal-metal center layer distance. The equilibriumun-modified materials layer distance is specified as well as theestimated 1C rate performance for a representative 100 nm radiuselectrode particle.

FIG. 4 is a graph of calculated diffusivity by first principles nudgedelastic band calculations for a single Li ion in layered V₂O₅ as afunction of the metal-metal center layer distance. The equilibriumun-modified materials slab layer distance is specified as well as theestimated 1C rate performance for a representative 100 nm radiusparticle.

FIG. 5 is a schematic diagram of an example onium ion. The moieties R¹,R², R³, and R⁴ each represent an alkyl, aryl, alkenyl, alkynyl group, ormixture thereof, and N+ can be substituted for other cation centersincluding, but not limited, to P, As, Sb, Bi, F, and S.

FIG. 6 is a diagram of a pyrrolidinium ion.

FIG. 7 is a graph of the behavior of a three electrode pouch cellcontaining a increased-layer spacing modified V₂O₅ material incorporatedinto a working electrode and displaying nucleation of a new “scaffolded”phase due to P13 onium cation co-intercalation during discharge one ascompared to subsequent voltage profiles demonstrating facile Mgintercalation. The cell was cycled between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference at 80° C.

FIG. 8 is a diagram showing the X-ray diffraction (XRD) spectra ofincreased-layer spacing V₂O₅ cathodes cycled in P13-TFSI/Mg-TFSIelectrolyte indicating the structural changes corresponding to themodification of the material. For reference, a representative XRDpattern of an electrode containing the un-modified V₂O₅ material isshown in comparison to the intercalated (discharged) and de-intercalated(charged) cathode. The cathodes containing the modified materials show anew peak at 18° corresponding to the spreading of the layers within thiscathode host structure.

FIG. 9 is a graph that shows the comparison of capacity of dischargedcells containing modified layered cathode material to the transientmagnesium quantified by elemental analysis.

FIG. 10 is a graph that shows the comparison of the scaffolding P13 ioncontent and the transient magnesium content in charge and dischargedcells.

FIG. 11 is a graph that demonstrates the voltage profile of a cell witha V₂O₅ layered cathode material in an electrolyte containing only thescaffolding ion P13 in TFSI, and no magnesium salt. The voltage ismeasured versus the Ag/Ag⁺ quasi-reference.

FIG. 12 is a graph that shows the voltage profile for the firstdischarge and subsequent charge of a cell with a V₂O₅ layered cathodematerial in an electrolyte containing P13-TFSI in the electrolyte, butno magnesium salt. The voltage is measured vs. an Ag/Ag⁺ quasi-referenceelectrode. The cell was discharged to −1 V (vs. Ag quasi) and charged to0.7 V (vs. Ag quasi) galvanostatically at 200 mA/g. A discharge capacityof approximately 60 mAh/g, and a subsequent charge of 20 mAh/g areobserved, which are attributed to semi-reversible intercalation of theonium cation (P13).

FIG. 13 is a graph that shows a comparison of the nitrogen content incathodes of cycled cells (ending in both discharged and charged states)and non-cycled cells (i.e., only soaked in electrolyte containingP13-TFSI). Nitrogen content is quantified using LECO time-of-flight massspectrometry.

FIG. 14 is a graph that provides an estimate for the quantity of P13onium cation (i.e., P13_(x)V₂O₅) in the V₂O₅ host derived from the ppmlevel of nitrogen relative to the vanadium content in the electrode. Itis compared to the amount of P13 estimated to be in the cathode basedupon residing cell capacity (i.e. capacity associated with Coulombicinefficiency).

FIG. 15 is a graph that depicts the voltage profile of an electrodepouch cell containing a V₂O₅ working electrode and displaying nucleationof a new phase due to ethyl-dimethyl-propyl-ammonium “N1123” scaffoldingion co-intercalation during discharge one as compared to subsequentvoltage profiles demonstrating facile Mg intercalation. The cell wascycled between −1.2 and 0.7 V versus the Ag/Ag⁺ quasi-reference at roomtemperature.

FIG. 16 is a graph that depicts the voltage profile of a electrode pouchcell containing a V₂O₅ working electrode and displaying nucleation of anew phase due to 1-butyl-2,3-dimethylimidazolium “BDMI” scaffolding(onium) cation co-intercalation during discharge one as compared tosubsequent voltage profiles demonstrating facile Mg intercalation. Thecell was cycled between −1.2 and 0.7 V versus the Ag/Ag⁺ quasi-referenceat room temperature.

FIG. 17 is a graph that depicts the voltage profile of a electrode pouchcell containing a layered MoO₃ working electrode and displayingnucleation of a new phase due to structural modification (“scaffolding”)of the layered structure using the P13 co-intercalation during the firstdischarge and subsequent voltage profiles demonstrating facile Mgintercalation. The cell was cycled between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference at room temperature.

FIG. 18 is a graph that depicts the voltage profile of a pouch cellcontaining a layered LiV₃O₈ working electrode and displaying nucleationof a new modified P13-LiV₃O₈ due to co-intercalation with thescaffolding P13 onium cation of the layered structure during the firstdischarge. Subsequent voltage profiles demonstrating facile Mgintercalation. The cell was cycled between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference at room temperature.

FIG. 19 is a graph that depicts the voltage profile of a pouch cellcontaining a scaffolded layered P13_(x)V₂O₅ synthesized via ex-situreaction, which demonstrates high specific capacity during galvanostaticcycling. Note this electrolyte contains no additional onium ion.

FIG. 20 is a diagram showing a bi-cell design.

FIG. 21 is a diagram showing a pouch cell design.

FIG. 22 is a diagram showing a spiral-wound cylindrical cell design.

FIG. 23 is a diagram showing a single layer button cell design.

DETAILED DESCRIPTION

The present invention relates to layered materials with a slab spacingof said layered material being within a specific range of values optimalfor multi-valent ion diffusion. More specifically, the invention isdirected to rechargeable magnesium batteries with high energy densityand high power and the method described herein aims to increase thediffusivity of magnesium ions inside a host layered positive electrodematerial, while still maintaining structural integrity and stablecycling performance of said electrode material.

Multi-valent ion intercalation is expected to increase the accessibleenergy density of the positive electrode material as more than oneelectron per intercalated ion can be utilized.

In contrast to lithium and other alkali metals, the abundance of somealkaline earth metals, such as Mg metal and readily available compoundscontaining Mg, is expected to provide significant cost reductionrelative to Li-ion batteries, and are expected to provide superiorsafety and waste disposal characteristics.

Positive electrode layered materials that allow facilitated diffusion ofmulti-valent ions are described. Improved layered cathode materials areexpected to provide for the production of a practical, rechargeablemulti-valent (e.g., magnesium) battery, which are expected to be saferand cleaner, and more durable, efficient and economical than heretoforeknown.

The present invention successfully addresses the shortcomings in termsof multi-valent ionic mobility inside layered positive electrodematerials and provides the basis for the production of a viable,rechargeable high-energy density magnesium battery.

In this description is provided a specific range of inter-layerdistances in layered electrode materials which optimize the mobility ofthe multi-valent ion (as distinct from a uni-valent ion, such as Li⁺,Na⁺or K⁺) that can be chosen from the alkaline earth, scandium or boronfamily (e.g., Mg²⁺, Ca²⁺, Al³⁺, Y³⁺, etc) within the host electrodematerial and thus improves the operation of a multi-valentelectrochemical cell. To achieve this, according to one aspect of theinvention, there is provided a positive electrode containing apositive-electrode active material with a layered structure; a negativeelectrode disposed opposite to the positive electrode and containing anegative-electrode active material which allows plating and dissolutionof multi-valent ions; and a non-aqueous electrolyte disposed between thepositive and negative electrode, containing a non-aqueous solvent aswell as a multi-valent cation salt. According to another aspect of theinvention, there is a modification of the positive electrode materialsuch that the layer spacing of the modified structure is larger than 4.8Å.

The layered active-electrode material has a structure that permitsdiffusion paths of multi-valent ions in two-dimensional shapes whilestill maintaining high energy density per volume unit. According toanother aspect of the invention, the modified layer spacing of thepositive electrode material is not larger than 8 Å.

According to one aspect of the invention, modified layered cathodematerials with expanded spacing using a scaffolding agent inside thelayers in two-dimensional multi-valent diffusing positive electrodematerials are described. An expanded interlayer spacing is expected toimprove multi-valent ionic diffusion in layered materials. Slowdiffusion of ions in layered materials is believed to represent alimitation for practical use as positive electrode materials inrechargeable multi-valent ion electrochemical cells.

In use, the layered cathode material can be treated to have a modifiedinterlayer spacing at any time, including at a time before the electrodematerial is placed in a rechargeable electrochemical cell, at a timeafter the electrode material is placed in an electrochemical cell, andat such time that the material is made operational within anelectrochemical cell.

The scaffolding agent can be inorganic molecules or cations that areelectrochemically inactive in the cell operating voltage.

The scaffolding agent can be an organic molecule or organic cation.

One such family of scaffolding agents are onium compounds. Oniumcompounds are cations derived by the protonation of mononuclear parenthydrides of elements of the nitrogen group (Group 15 of the PeriodicTable of the Elements), chalcogens (Group 16), or halogens (Group 17),and similar cations derived by the substitution of hydrogen atoms in theformer by other groups, such as organic radicals, or halogens, forexample tetramethylammonium, and further derivatives having polyvalentadditions, such as iminium and nitrilium.

Onium ions can contain a long (C₆+) chain radical. Examples of suchsuitable organic C₆+ onium ion molecules include primary, secondary,tertiary, or quaternary ammonium, sulfonium, phosphonium, oxonium or anyion of an element in Groups V or VI of the periodic table of elements.An example of an organic onium cation is presented in FIG. 5.

The long chain can act as a spacing/compartmentalization agent.According to one embodiment, the spacing agent has at least one bindingsite capable of ion-exchanging or replacing Li⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺orother inorganic cations that may occur within the layer spacing of thetarget material.

In one embodiment, the modification of the layered cathode materialinvolves co-intercalation of an onium ion, such asN-methyl-N-propylpyrrolidinium (known as “P13”), together with analkaline earth ion, such as Mg²⁺, into the host material during thefirst discharge. The intercalation increases the layer spacing of thehost positive electrode material and thereby facilitates magnesiumdiffusion.

In another embodiment, the active layered cathode material can beelectrochemically pre-treated in an electrolyte solution containingonium ions, discharged to a desirable degree and then transferred to thebattery cell. In either embodiment, an advantageous result of theprocess is a positive layered electrode host material with expandedlayer spacing, which enables fast diffusion of multi-valent ions forrechargeable electrochemical cells.

In yet another embodiment, the active layered cathode material can bechemically pre-treated in a solution containing onium ions, so as tochemically intercalate within the layers enabling a host material withexpanded layer spacing and fast diffusion of multi-valent ions.

Hence, according to further features in preferred embodiments of theinvention described below, the electrolyte containing onium ionsaccording to the present invention is incorporated into specificelectrochemical cells containing an appropriate anode and layeredcathode pair.

In one aspect, a compound of formula Mg_(a)M_(b)X_(y) for use aselectrode material in a magnesium battery is described, wherein thematerial is a layered crystalline compound having the general formulaMg_(a)M_(b)X_(y), wherein “M” is a metal cation, or mixture of metalcations and “X” is an anion or mixture of anions. In some embodiments, Xis oxygen (O), sulfur (S), selenium (Se) or fluoride (F), or mixturesthereof. The structures can have a close-packed lattice of O, S, Se, orF, with layers of octahedrally-coordinated metals that are capable ofbeing oxidized during Mg extraction (for example, selected from thegroup consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Nb, Sn, Sb, Bi Ag, ormixtures thereof) alternating with layers of fully or partially occupiedmagnesium sites. In certain embodiments, M is one or more transitionalmetals selected from the group consisting of Cr, Mn, Ni, Co, andmixtures thereof; and X is one or more anions selected from the groupconsisting of O, S, F, and mixtures thereof. In other embodiments, M isone or more transitional metals selected from the group consisting of V,Cr, Mn, Fe, Ni, Co, Cu, Mo, Nb, Sn, Sb, Bi Ag and mixtures thereof; andX is one or more anions selected from the group consisting of O, S, F,and mixtures thereof.

In some embodiments, the compound is in an oxidized state and a is about0. In some embodiments, the compound is in a reduced state and a is inthe range of 1 to 2. In some embodiments, b is about 1 and y is about 2.In other embodiments, b is about 2 and y is about 4. In yet otherembodiments, b is about 1 and y is in the range of 2 to 9.

In one or more embodiments, the material includes layered transitionmetal oxides, sulfides, fluorides, chlorides and selenides, or anymixtures thereof with layers of octahedrally-coordinated transitionmetals alternating with layers of fully or partially occupied magnesiumsites. In particular embodiments, the layered compound include oxidescontaining transition metals such as V, Cr, Ni, Mn, Co, or mixturesthereof on the transition metal site. Examples of compositions that areable to insert nearly one magnesium ion per two transition metal ionsinclude CoMn₂O₆ and CrS₂. In other embodiments, the material includessulfides and selenides containing V, Mn, or Cr as the transition metals.These sulfide and selenide materials provide lower voltage (˜0.25 V to˜2.25 V vs. Mg/Mg²⁺) and may also be useful in magnesium insertionanodes or exhibit superior stability in certain electrolytes.

According to another embodiment, the scaffolding ion isN-propyl-N-methylpyrrolidinium (P13) which is electrochemically insertedinto layered V₂O₅ whereby the layer spacing, relevant for Mg²⁺diffusion,of the V₂O₅ host is expanded.

While various metals are suitable as anodes for the electrolyticsolution, including magnesium, aluminum, calcium, yttrium and zirconium,a particularly preferred embodiment of a battery according to thepresent invention includes the electrolyte according to the presentinvention, a magnesium metal anode and a magnesium insertion compoundcathode.

In some embodiments, the positive electrode layer further comprises anelectronically conductive additive. Non-limiting examples ofelectronically conductive additives include carbon black, Super P, SuperC65, Ensaco black, Ketjen black, acetylene black, synthetic graphitesuch as Timrex SFG-6, Timrex SFG-15, Timrex SFG-44, Timrex KS-6, TimrexKS-15, Timrex KS-44, natural flake graphite, carbon nanotubes,fullerenes, hard carbon, or mesocarbon microbeads.

In some embodiments, the positive electrode layer further comprises apolymer binder. Non-limiting examples of polymer binders includepoly-vinylidene fluoride (PVdF), poly(vinylidenefluoride-co-hexafluoropropene) (PVdF-HFP), Polytetrafluoroethylene(PTFE), Kynar Flex 2801, Kynar Powerflex LBG, and Kynar HSV 900, orTeflon.

Negative electrodes used in conjunction with the present inventioncomprise a negative electrode active material that can accept Mg-ions.Non-limiting examples of negative electrode active material for the Mgbattery include Mg, common Mg alloys such as AZ31, AZ61, AZ63, AZ80,AZ81, AZ91, AM50, AM60, Elektron 675, ZK51, ZK60, ZK61, ZC63, M1A, ZC71,Elektron 21, Elektron 675, Elektron, Magnox, or insertion materials suchas Anatase TiO₂, rutile TiO₂, Mo₆S₈, FeS₂, TiS₂, MoS₂. It is believedthat alloys of Mg with one or more of the elements Al, Ca, Bi, Sb, Sn,Ag, Cu, and Si can also be used.

In some embodiments, the negative electrode layer further comprises anelectronically conductive additive. Non-limiting examples ofelectronically conductive additives include carbon black, Super P, SuperC65, Ensaco black, Ketjen black, acetylene black, synthetic graphitesuch as Timrex SFG-6, Timrex SFG-15, Timrex SFG-44, Timrex KS-6, TimrexKS-15, Timrex KS-44, natural flake graphite, carbon nanotubes,fullerenes, hard carbon, or mesocarbon microbeads.

In some embodiments, the negative electrode layer further comprises apolymer binder. Non-limiting examples of polymer binders includepoly-vinylidene fluoride (PVdF), poly(vinylidenefluoride-co-hexafluoropropene) (PVdF-HFP), Polytetrafluoroethylene(PTFE), Kynar Flex 2801, Kynar Powerflex LBG, and Kynar HSV 900, orTeflon.

In some embodiments, the electrochemical cell used in conjunction withan inorganic electrolyte described herein comprises a positive electrodecurrent collector comprising carbonaceous material or metal coated withcarbonaceous material or metal coated with a barrier over-layerproviding improved chemical and electrochemical inertness. In someembodiments, the electrochemical cell described herein comprises anegative electrode current collector comprising carbonaceous material ormetal coated with carbonaceous material or metal coated with a barrierover-layer providing improved chemical and electrochemical inertness.

In other embodiments, the electrochemical cell described hereincomprises positive and negative electrode current collectors comprisingcarbonaceous material or metal coated with carbonaceous material.

FIG. 20 is a diagram showing a bi-cell design. FIG. 21 is a diagramshowing a pouch cell design. In some embodiments, the electrochemicalcell disclosed herein is a prismatic, or pouch, bi-cell consisting ofone or more stacks of a positive electrode which is coated with activematerial on both sides and wrapped in porous polypropylene or glassfiber separator, and a negative electrode folded around the positiveelectrode wherein one or both current collectors comprise carbonaceousmaterials. The stack(s) are folded within a polymer coated aluminum foilpouch, dried under heat and/or vacuum, filled with electrolyte, andvacuum and heat sealed. In some embodiments of the prismatic or pouchcells used in conjunction with the electrolyte described herein, anadditional tab composed of a metal foil or carbonaceous material of thesame kind as current collectors described herein, is affixed to thecurrent collector by laser or ultrasonic welding, adhesive, ormechanical contact, in order to connect the electrodes to the deviceoutside the packaging.

FIG. 22 is a diagram showing a spiral-wound cylindrical cell design. Insome embodiments, the electrochemical cell used in conjunction with theelectrolyte disclosed herein is a wound or cylindrical cell consistingof wound layers of one or more stacks of a positive electrode which iscoated with active material on one or both sides, sandwiched betweenlayers of porous polypropylene or glass fiber separator, and a negativeelectrode wherein one or both current collectors comprise carbonaceousmaterials. The stack(s) are wound into a cylindrical roll, inserted intothe can, dried under heat and/or vacuum, filled with electrolyte, andvacuum and welded shut. In some embodiments of the cylindrical cellsdescribed herein, an additional tab composed of a metal foil orcarbonaceous material, or metal coated with carbonaceous material of thesame kind as current collectors described herein, is affixed to thecurrent collector by laser or ultrasonic welding, adhesive, ormechanical contact, in order to connect the electrodes to the deviceoutside the packaging.

FIG. 23 is a diagram showing a single layer button cell design. In someembodiments, the electrochemical cell disclosed herein is a button orcoin cell battery consisting of a stack of negative electrode, porouspolypropylene or glass fiber separator, and positive electrode disks sitin a can base onto which the can lid is crimped. In other embodiments,the electrochemical cell used in conjunction with the electrolytedisclosed herein is a stacked cell battery. In other embodiments, theelectrochemical cell disclosed herein is a prismatic, or pouch, cellconsisting of one or more stacks of negative electrode, porouspolypropylene or glass fiber separator, and positive electrodesandwiched between current collectors wherein one or both currentcollectors comprise carbonaceous materials. The stack(s) are foldedwithin a polymer coated aluminum foil pouch, vacuum and heat dried,filled with electrolyte, and vacuum and heat-sealed.

EXAMPLE 1

This example provides ionic diffusivity data estimated fromfirst-principles nudged-elastic band calculations of Mg mobility inlayered V₂O₅.

FIG. 1A shows a schematic illustration of a typical layered electrodematerial where the Mg ions are indicated and the slab inter-layerdistance as measured by the metal-metal center distance (slab space) isdefined.

FIG. 1B is a schematic diagram of a layered material having a firstplurality of layers of inorganic material 105, 105′, 105″ separated by asecond plurality of units of an organic species situated on interveningplanes 110, 110′. The units of the organic species do not necessarilyhave to provide a layer of contiguous organic units, but rather thereneed to be enough of such units of the organic species that layers ofinorganic material are separated by a distance that is sufficient toallow rapid insertion and removal of multi-valent positive ions such asMg²⁺, Al³⁺and other such ions so that charging and discharging of anenergy storage device (such as a secondary battery) can be performed atsuitable rates, such as C/15, C/10, C/5, or C discharge rates.

FIG. 2 shows the estimated dilute-limit diffusivity of a Mg ion movingthrough the layer of V₂O₅ as a function of the slab (layer) spacedistance. The unmodified slab distance as well as the diffusivitycorresponding to 1C rate for a 100 nm electrode particle are indicated.

FIG. 2 exemplifies the strong influence of layer space distance on theMg diffusivity and that there exist a specific range of layer spacing inV₂O₅, e.g., 4.8 Å to 6 Å, for which sufficient Mg mobility (1C) forenergy storage applications is enabled. In a preferred embodiment forV₂O₅, the range of layer spacing is in the range of 4.8 Å to 6 Å.

EXAMPLE 2

This example provides ionic diffusivity data estimated fromfirst-principles nudged-elastic band calculations of Mg mobility inlayered MnO₂.

FIG. 3 shows the estimated dilute-limit diffusivity of a Mg ion movingthrough the layer of MnO₂ as a function of the slab (layer) spacedistance (as defined by FIG. 1A). The unmodified slab distance as wellas the diffusivity corresponding to 1C rate for a 100 nm electrodeparticle are indicated.

FIG. 3 exemplifies the strong influence of layer spacing distance on theMg diffusivity and that there exist a specific range of layer spacing inMnO₂, e.g., 4 Å to 8 Å, for which sufficient Mg mobility (1C) for energystorage applications is enabled.

EXAMPLE 3

This example provides diffusivity data estimated from first-principlesnudged-elastic band calculations of Li ion mobility in layered V₂O₅.

FIG. 4 shows the estimated dilute-limit diffusivity of a Li ion movingthrough the layer of V₂O₅ as a function of the slab (layer) spacedistance (as defined by FIG. 1A) The unmodified slab distance as well asthe diffusivity corresponding to 1C rate for a 100 nm electrode particleare indicated.

FIG. 4 exemplifies the that Li ions have good diffusivity irrespectiveof large changes in layer space distance and that, in contrast to Mgions, sufficient Li ionic mobility (1C) for energy storage applicationsis enabled for all reasonable layer space distances. In a preferredembodiment, the range of layer spacing is in the range of 4.8 Å to 5.5Å.

EXAMPLE 4

This example provides a combined electrochemical, structural, andelemental analysis of cycled cells demonstrating modification of layeredV₂O₅ through co-intercalation of P13 scaffolding ions which facilitatesmagnesium intercalation into V₂O₅ upon discharge. Thereafter, theelectrochemical specific capacity is largely associated with reversibleintercalation of Mg.

FIG. 7 shows a representative voltage profile of a three electrode pouchcell containing a V₂O₅ working electrode in an electrolyte containingboth magnesium salt and the scaffolding ion. Cycle 1 dischargedemonstrates the nucleation (i.e., temporary ‘dip’ in voltage) of a newphase due to P13 scaffolding ion co-intercalation. This is in contrastto the subsequent two to four cycles, which no longer demonstrate thenucleation feature, and appear to correspond with facile Mgintercalation. The cell was cycled between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference.

To confirm that the majority of capacity is due to Mg intercalation sixcells containing V₂O₅ cathodes and 0.4M Mg-TFSI in P13-TFSI electrolytewere constructed and cycled five times between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference at 80° C. After cycling each cathode wasstructurally analyzed with X-ray diffraction (XRD) and elementalanalysis (DCP-AES) for quantification of Mg and V. Table 1 shows thatfour cells were terminated in the discharged state and two cells wereterminated in the charged state. For each cell the expected magnesium tovanadium ratio based upon the final specific capacity of theelectrochemical cycling is compared to the Mg/V ratio determined throughelemental analysis.

Elemental analysis confirms magnesium content corresponds well with thecharge passed during electrochemical cycling. Fluctuations around theexpected Mg/V atomic ratio based on electrochemical testing are withinknown errors in estimation of cathode mass and residual electrolyte dueto incomplete rinsing and similar sources of systematic error. Given theappreciable changes in Mg/V ratios between charge and discharged cellsit is clear Mg is being transferred in the electrochemical discharge ofthese cells.

TABLE 1 Comparison of the Mg/V ratio expected from electrochemicaltesting of cells and corresponding elemental analysis. State of Mg/VCurrent Charge Mg/V actual Density End State (mAh/g) expected (ICP)(mA/g) Discharge 101 0.168 0.148 20 Discharge 106 0.177 0.141 20Discharge 103 0.172 0.147 20 Discharge 107 0.178 0.133 20 Charge 0 00.043 20 Charge 0 0 0.048 20

FIG. 8 depicts transitions in the XRD spectra of cells cycled in theP13-TFSI/Mg-TFSI electrolyte. The results confirm structural changes tothe interlayer spacing of the host material; V₂O₅ in this case. Forreference, a representative XRD pattern of a virgin electrode is shown.Upon discharge, a clear diffuse peak (marked by arrows) is observed near18° 2-theta. Upon charge, the diffuse peak shifts to 19° 2-thetaindicating a semi-reversible structural change. Of note, the (200) and(110) peaks of V₂O₅ do not appear to shift appreciably, while anattenuation of the (001) peak is observed in both the charged anddischarged cells. This is consistent with the layer-spacing modifying(“scaffolding”) ion P13 co-intercalating with Mg into V₂O₅ layers, andremaining in the V₂O₅ host while Mg de-intercalates during charge. Suchan effect would modify all (001) reflections more significantly than(hk0) reflections. Additionally, the V₂O₅ starting material is clearlynot recovered on charge. XRD patterns of charged cells display a diffusepeak at 19° 2-theta.

EXAMPLE 5

This example provides a combined electrochemical and elemental analysisof cycled cells demonstrating intercalation of the P13 scaffolding ioninto layered cathodes such as V₂O₅ is largely irreversible in thepresence of magnesium ions and therefore constitutes a stablemodification of the cathode host layered structure even during Mg ioncycling. Pouch cells were constructed using layered V₂O₅ as the workingelectrode and an electrolyte containing 0.4 M Magnesiumbis(trifluoromethanesulfonyl)imide (MgTFSI) inN-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13TFSI) as the electrolyte. All cells underwent five galvanostatic cyclesat 10 mA/g between −1.2 V and +0.7 V vs. an Ag/Ag⁺ quasi-referenceelectrode. The water content was below 150 ppm in the electrolyte. Aftercycling, or sitting while the remainder of the test set was cycled, thecharged, discharged, and non-cycled cells were opened in an Argon filledglovebox, and the cathodes removed and rinsed. All cathodes wereanalyzed for both nitrogen (by LECO) and magnesium (by DCP-AES) content.For each discharged cell, the amount of magnesium that was actuallyinvolved in cycling was calculated from the difference in magnesiumcontent of the particular discharged cathode and the average magnesiumcontent of all the charged cathodes. This difference is known as thetransient magnesium content. The amount of transient magnesium in thedischarged cathodes (expressed as a capacity) is compared to the actualfinal discharge capacity that was measured electrochemically in FIG. 9.

The nitrogen content was also measured for the same cathodes (fromcharged, discharged and non-cycled cells). The charged and dischargedcells are expected to contain nitrogen due to intercalated P13 ions.Although the samples are rinsed, trace electrolyte and sorption ofatmospheric nitrogen will influence the quantification of nitrogencontent. Therefore non-cycled cells serve as a blank, so the averagenitrogen content of the non-cycled cells was subtracted from thenitrogen detected in the charged and discharged cells, to give theamount of nitrogen solely due to intercalated P13 for each of thecharged and discharged cells. Note that, as expected, XRD indicates thatnon-cycled cells did not intercalate P13 simply by immersion insolution. The P13 content derived from the presence of nitrogen in thecathodes can be expressed as specific capacity (mAh/g) by assuming a oneelectron per P13 inserting into the layered host. FIG. 10 depicts theamount of P13 in the cathodes compared to the amount of transientmagnesium. Note that charged cells by definition do not contain anytransient magnesium. This data demonstrates that the amount of P13 inthe cathodes is very low relative to the amount of transient magnesium.

EXAMPLE 6

This example provides a combined electrochemical and elemental analysisof cycled cells demonstrating intercalation of the P13 onium ion intolayered cathodes such as V₂O₅ is largely irreversible even in theabsence of magnesium ions.

Pouch cells were constructed using layered V₂O₅ as the working electrodeand an electrolyte containing N-propyl-N-methylpyrrolidiniumbis(trifluoromethanesulfonyl)imide (P13 TFSI) as the electrolyte with noMg salt in the electrolyte. An Ag/Ag⁺ quasi-reference electrode was alsoemployed.

FIG. 11 shows the discharge of the cell containing V₂O₅ in electrolytecontaining P13, but no Mg salt. This cell is discharged to −1 V vs.Ag/Ag⁺ quasi-reference electrode. The discharge capacity isapproximately 60 mAh/g and is attributed to intercalation of the oniumion (P13) as no Mg was present in the cell.

Similarly FIG. 12 shows the discharge and subsequent charge of a cellcontaining V₂O₅ cathode. The cell is first discharged to −1 V vs. Ag/Ag⁺quasi-reference electrode and subsequently charged to 0.7 V vs. Ag/Ag⁺quasi-reference galvanostatically at 200 mA/g. The discharge capacity isapproximately 60 mAh/g while the subsequent charge capacity is 20 mAh/gthus demonstrating that the majority of intercalation due to the P13onium ion is irreversible.

Subsequently, the V₂O₅ cathodes from the cells with voltage profilesdisplayed in FIG. 11 and FIG. 12 were analyzed along with similar cellsfor nitrogen content using LECO time-of-flight-mass spectrometry. Theaim was is to determine if there are elevated nitrogen levels in thecathode due to intercalation of P13. Each P13 ion contains one nitrogenatom and there is no other appreciable nitrogen source within thesecells. FIG. 13 illustrates that cycled cells (both those that end indischarge and charge) contain significantly more nitrogen than thenon-cycled cells thus providing additional evidence that P13 and otheronium ions irreversibly intercalate into layered materials.

The amount of P13 in the V₂O₅ host can be estimated and expressed asP13_(x)V₂O₅ by converting the measured quantity (ppm) of nitrogen to anabsolute amount assuming the mass of the cathode is known and entirelyconsumed during LECO analysis. FIG. 14 provides comparison of these P13content values to the amount of P13 estimated to be in the cathode basedon cell capacity. It should be noted that these estimates of x inP13_(x)V₂O₅ constitute a maximum bound because the specific capacitiesmay be inflated by side (parasitic) electrochemical reactions while theN content may be high if residual electrolyte remains on the sample, orby the sorption of N₂ from the atmosphere. Note that the non-cycledcells also returned positive N values. Nonetheless, as an approximation,FIG. 14 demonstrates that x≈0.16, or 0.1 if one corrects for the Nlevels detected in the non-cycled cells.

EXAMPLE 7

This example provides evidence of that the desired modifications of thelayer spacing can be achieved using a variety of different ions thatscaffold the host electrode layer. Similarly, after co-intercalation theelectrochemical specific capacity is largely associated with reversibleintercalation of Mg while the scaffolding ion remains within the layersof V₂O₅.

FIG. 15 shows a representative voltage profile of a three electrodepouch cell containing a layered V₂O₅ working electrode in an electrolytecontaining both a magnesium salt and scaffolding ions that can modifythe layer spacing by irreversible intercalation. The cycle 1 dischargeshows nucleation of a new phase due to the scaffolding ionco-intercalation. This is in contrast to the subsequent two to tencycles, which no longer demonstrate the nucleation feature, and appearto correspond with facile Mg intercalation. The cell was cycled between−1.2 and 0.7 V versus the Ag/Ag⁺ quasi-reference. The ion utilized tomodify the layer spacing (scaffold) of the electrode material in thiscell is ethyl-dimethyl-propyl-ammonium “N1123.”

FIG. 16 shows a representative voltage profile of a three electrodepouch cell containing a layered V₂O₅ working electrode in an electrolytecontaining both a magnesium salt and ions that can scaffold the layerspacing by irreversible intercalation. The cycle 1 discharge showsnucleation of a new phase due to the scaffolding ion co-intercalation.This is in contrast to the subsequent two to ten cycles, which no longerdemonstrate the nucleation feature, and appear to correspond with facileMg intercalation. The cell was cycled between −1.2 and 0.7 V versus theAg/Ag⁺ quasi-reference. The scaffolding ion utilized in this cell is1-butyl-2,3-dimethylimidazolium “BDMI.”

EXAMPLE 8

This example provides evidence of concomitant scaffolding ion andmagnesium cation intercalation into layered cathode materials other thanV₂O₅ using scaffolding ions (i.e., P13). Similar to the V₂O₅ cells,after co-intercalation the electrochemical specific capacity is expectedto be largely associated with reversible intercalation of Mg while thescaffolding ion remains within the layers of V₂O₅.

FIG. 17 shows a representative voltage profile of a three electrodepouch cell containing a layered, orthorhombic phase, MoO₃ workingelectrode in an electrolyte containing both magnesium salt and the P13scaffolding ion. The cycle 1 discharge shows nucleation of a new phasedue to the P13 scaffolding ion co-intercalation. This is in contrast tothe subsequent cycles two and three, which also no longer demonstratethe nucleation feature, and appear to correspond with facile Mgintercalation. The cell was cycled between −1.6 and 0.6 V versus theAg/Ag⁺ quasi-reference.

FIG. 18 shows a representative voltage profile of a three electrodepouch cell containing a layered LiV₃O₈ working electrode in anelectrolyte containing both a magnesium salt and scaffolding ions. Thecycle 1 discharge shows nucleation of a new phase due to the P13scaffolding cation co-intercalation. This is in contrast to thesubsequent two to ten cycles, which no longer demonstrate the nucleationfeature, and appear to correspond with facile Mg intercalation. The cellwas cycled between −1.2 and 0.7 V versus the Ag/Ag⁺ quasi-reference.

EXAMPLE 9

This example presents demonstration of a process for ex-situ structuralmodification of a layered cathode material wherein scaffolding ionsinsert between the layers of a material such as V₂O₅. A typical reactioninvolves adding 0.50 grams (0.0027 moles) of V₂O₅, 0.56 grams (0.0014moles) of N-methyl, N-propyl pyrrolidiniumbis(trifluoromethanesulfonyl)imide (P13TFSI) and 3 ml of Ethanol in a500 ml beaker. Subsequently, with vigorous stirring, 10 ml of 35 wt %H₂O₂ is added dropwise to the mixture at room temperature. The reactionis very exothermic and is completed in less than 5 minutes.

The product is then collected and allowed to air dry overnight. FIG. 19depicts the voltage profile for the first ten cycles of a cellcontaining ex-situ synthesized P13_(x)V₂O₅ as the active cathodematerial and an electrolyte containing only MgTFSI salt (i.e., noscaffolding ions). Note that no nucleation features are observed duringthe first cycle discharge and facile magnesium intercalation isobserved. This data was collected employing galvanostatic cycling andthe voltage is measure using an Ag/Ag⁺ quasi-reference electrode wasalso employed.

Theoretical Discussion

Although the theoretical description given herein is thought to becorrect, the operation of the devices described and claimed herein doesnot depend upon the accuracy or validity of the theoretical description.That is, later theoretical developments that may explain the observedresults on a basis different from the theory presented herein will notdetract from the inventions described herein.

Any patent, patent application, or publication identified in thespecification is hereby incorporated by reference herein in itsentirety. Any material, or portion thereof, that is said to beincorporated by reference herein, but which conflicts with existingdefinitions, statements, or other disclosure material explicitly setforth herein is only incorporated to the extent that no conflict arisesbetween that incorporated material and the present disclosure material.In the event of a conflict, the conflict is to be resolved in favor ofthe present disclosure as the preferred disclosure.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail may be affected therein without departing from the spirit andscope of the invention as defined by the claims.

What is claimed is:
 1. An energy-storage apparatus, comprising: an anodeconfigured to accept Mg ions from an electrolyte and to release Mg-ionsto said electrolyte, said anode having at least one anode electricalconnection on an external surface of said energy-storage apparatus, andhaving at least one anode surface within said energy-storage apparatus;a cathode comprising a layered crystalline compound comprising atransition metal, wherein an interlayer metal-metal distance in saidlayered crystalline compound is 4.8 Angstrom or more, said layeredcrystalline compound having at least one cathode electrical connectionon an external surface of said energy-storage apparatus and having atleast one cathode surface within said energy-storage apparatus; and saidelectrolyte comprising a magnesium-bearing electrolyte in contact withsaid at least one anode surface within said energy-storage apparatus,and in contact with said at least one cathode surface within saidenergy-storage apparatus.
 2. The energy-storage apparatus of claim 1,wherein said cathode comprising a layered crystalline compound comprisesa compound having the chemical formula Mg_(a)M_(b)X_(y), wherein M is ametal cation or a mixture of metal cations, X is an anion or mixture ofanions, a is in the range of 0 to about 2, b is in the range of about 1to about 2, and y ≦9.
 3. The energy-storage apparatus of claim 1,wherein at least one of said anode and said cathode further comprises anelectronically conductive additive.
 4. The energy-storage apparatus ofclaim 1, wherein at least one of said anode and said cathode furthercomprises a polymer binder.
 5. The energy-storage apparatus of claim 1,wherein said anode configured to accept and release Mg-ions comprises amaterial selected from the group consisting of Mg, Mg alloys AZ31, AZ61,AZ63, AZ80, AZ81, AZ91, AM50, AM60, Elektron 675, ZK51, ZK60, ZK61,ZC63, M1A, ZC71, Elektron 21, Elektron 675, Elektron, Magnox, and Mgalloys containing at least one of the elements Al, Ca, Bi, Sb, Sn, Ag,Cu, and Si.
 6. The energy-storage apparatus of claim 1, wherein saidanode configured to accept and release Mg-ions comprises insertionmaterials including one or more of Anatase TiO₂, rutile TiO₂, Mo₆S₈,FeS₂, TiS₂, and MoS₂ and combinations thereof.
 7. The energy-storageapparatus of claim 1, wherein at least one of said cathode and saidanode comprises a carbonaceous material.
 8. The energy-storage apparatusof claim 1, wherein said energy-storage apparatus is a secondarybattery.
 9. An energy-storage apparatus, comprising: an anode configuredto accept Mg ions from an electrolyte and to release Mg-ions to saidelectrolyte, said anode having at least one anode electrical connectionon an external surface of said energy-storage apparatus, and having atleast one anode surface within said energy-storage apparatus; a cathodecomprising a layered crystalline compound comprising a deliberatelyadded specie or species so that a layer spacing of said layeredcrystalline compound is modified to allow for magnesium ion diffusionsufficient to support at least a C/5 discharge rate of said energystorage apparatus, said layered crystalline compound having at least onecathode electrical connection on an external surface of saidenergy-storage apparatus and having at least one cathode surface withinsaid energy-storage apparatus; and said electrolyte comprising amagnesium-bearing electrolyte in contact with said at least one anodesurface within said energy-storage apparatus, and in contact with saidat least one cathode surface within said energy-storage apparatus. 10.The energy-storage apparatus of claim 9, wherein a layer spacing of saidlayered crystalline compound is modified to allow for magnesium iondiffusion sufficient to support at least a C/15 discharge rate of saidenergy storage apparatus.
 11. The energy-storage apparatus of claim 9,wherein said energy-storage apparatus is a secondary battery.
 12. Theenergy-storage apparatus of claim 9, wherein a shortest metal-metalinter-layer distance in said layered crystalline compound is larger than4.8 Angstrom.
 13. The energy-storage apparatus of claim 9, wherein ashortest metal-metal inter-layer distance in said layered crystallinecompound is smaller than 8 Angstrom.
 14. The energy-storage apparatus ofclaim 9, wherein a shortest metal-metal inter-layer distance in saidlayered crystalline compound is smaller than 12 Angstrom.
 15. Theenergy-storage apparatus of claim 9, wherein said cathode comprising alayered crystalline compound comprises a compound having the chemicalformula Mg_(a)M_(b)X_(y), wherein M is a metal cation, or mixture ofmetal cations and X is an anion or mixture of anions, and a is in therange of 0 to about 2, b is in the range of about 1 to about 2, and y≦9.
 16. The energy-storage apparatus of claim 9, wherein at least one ofsaid anode and said cathode further comprises an electronicallyconductive additive.
 17. The energy-storage apparatus of claim 9,wherein at least one of said anode and said cathode further comprises apolymer binder.
 18. The energy-storage apparatus of claim 9, whereinsaid anode configured to accept and release Mg-ions comprises a materialselected from the group consisting of Mg, Mg alloys AZ31, AZ61, AZ63,AZ80, AZ81, AZ91, AM50, AM60, Elektron 675, ZK51, ZK60, ZK61, ZC63, M1A,ZC71, Elektron 21, Elektron 675, Elektron, Magnox, and Mg alloyscontaining at least one of the elements Al, Ca, Bi, Sb, Sn, Ag, Cu, andSi.
 19. The energy-storage apparatus of claim 9, wherein said anodeconfigured to accept and release Mg-ions comprises insertion materialsselected from the group of insertion materials consisting of AnataseTiO₂, rutile TiO₂, Mo₆S₈, FeS₂, TiS₂, and MoS₂ and combinations thereof.20. The energy-storage apparatus of claim 9, wherein at least one ofsaid cathode and said anode comprises a carbonaceous material.